Hi Jim,
I have a follow up question for you. Are you able to build your apk to device or do you get the same error with the Android SDK? If you do get the same error when you build, take a look at your external tool settings in Unity Preferences. Make sure that you either have the corresponding SDK, JDK, and NDK installed either through Unity (By using the check boxes) or through an external application like Android studio (By setting the correct file path).
It might also be worth double checking you have android support installed by looking at your Unity version it Unity Hub.
